Disc drives are used for data storage in modem electronic products ranging from digital cameras to computers and network systems. Typically, a disc drive includes a mechanical portion and an electronics portion in the form of a printed circuit board assembly. The printed circuit board assembly provides mechanical control and a communication interface between the disc drive and its host.
Generally, the mechanical portion, or head-disc assembly, has a disc with a recording surface rotated at a constant speed by a spindle motor assembly and an actuator assembly positionably controlled by a closed loop servo system for use in accessing the stored data. The actuator assembly commonly supports a magnetoresistive read/write head that writes data to, and reads data from, the recording surface. Normally, the magnetoresistive read/write head uses an inductive element, or writer, to write data to and a magnetoresistive element, or reader, to read data from the recording surface.
The disc drive market continues to place pressure on the industry for disc drives with increased capacity at a lower cost per megabyte and higher rates of data throughput between the disc drive and the host. High performance disc drives achieve areal bit densities in the range of several gigabits per square centimeter (Gbits/cm2). Higher recording densities can be achieved by increasing the number of bits per centimeter stored along each information track, and/or by increasing the number of tracks per centimeter written across each recording surface. Increasing the number of tracks per centimeter on each recording surface generally requires improvements in servo control systems, which enable the read/write heads to be more precisely positioned relative to the information tracks. Increasing the number of bits per centimeter stored on each track generally requires improvements in the read/write channel electronics to enable data to be written to, and subsequently read from, the recording surface at a correspondingly higher frequency, which typically foster a need for improvements in the interface channel electronics for improved bit transfer rates.
Typically, interface channel electronics incorporate a parallel communication schema for data exchange. As is well known in the art, each line in a parallel communication cable has substantially distinct transmission efficiency. The transmission efficiency of any particular line is based on the impedance specific to that particular line. Variations in transmission efficiency, line to line, across a bus (such as a SCSI bus) introduces data skew, i.e., individual bits of data simultaneously transmitted, but received at slightly different times. Data skew, or signal offset, causes a reduction in transfer rate, because all the bits of a data transfer must be present for data re-assembly to complete the transfer.
Additionally, cabling electronic devices for parallel communication is costly, bulky and inhibits airflow internal to a computer enclosure. Prior solutions to these problems include conversion of ATA or SCSI data to packetized data and networking devices together. These solutions are inherently complex and necessitate embedding additional computational power into the interface electronics. Furthermore, because of packet overhead and the point-to-point requirement of the architecture, typically only about half of the interface bandwidth can be utilized. The point-to-point requirement of the architecture also precludes the full utilization of the bandwidth because only one device uses the channel at a time, thereby limiting the bandwidth resource to that device's maximum sustained data rate. For SCSI, some features would be lost with a full point-to-point bus implementation with multiple nodes interfaced on the bus. Additionally, a point-to-point networking architecture would necessitate changes in the SCSI specification to document the losses in a special subset of the SCSI specification and create a legacy problem for prior generation SCSI devices.
As such, challenges remain and a need persists for effective techniques for reducing cable bulk and eliminating data skew, while avoiding the creation of a legacy issue. It is to this and other features and advantages set forth herein that embodiments of the present invention are directed.